1. The Immune System

2. 2 Divisions of Immunity in Humans and Other Mammals
I. Innate Immunity “Non-Specific”
II. Acquired immunity “Specific”

3. A. Barrier Defenses

4. Skin

5. B. Cellular Defenses Microbes/antigens PHAGOCYTIC CELL Vacuole
Lysosome
containing
enzymes

6. There are different types of phagocytic cells:

7. Interstitial fluid Adenoid Adenoid Tonsil Tonsil Blood capillary Lymph
Fig. 43-7
Interstitial fluid
Adenoid
Adenoid
Tonsil
Tonsil
Blood
capillary
Lymph
nodes
Blood
capillary
Lymph
nodes
Spleen
Tissue
cells
Lymphatic
vessel
Spleen
Tissue
cells
Lymphatic
vessel
Peyer’s patches
(small intestine)
Peyer’s patches
(small intestine)
Appendix
Appendix
Figure 43.7 The human lymphatic system
Lymphatic
vessels
Lymph
node
Masses of
defensive cells
Lymph
node
Masses of
defensive cells

8. D. Inflammatory Responses
Fig
D. Inflammatory Responses
Pathogen
Splinter
Chemical
signals
Macrophage
Fluid
Mast cell
Capillary
Phagocytosis
Figure 43.8 Major events in a local inflammatory response
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Red blood cells
Phagocytic cell

9. II. Acquired immunity lymphocyte receptors provide pathogen-specific recognition

10. Fig. 43-9
B cells and T cells have receptor proteins that can recognize and bind to antigens
Antigen-
binding
site
Antigen-
binding site
Antigen-
binding
site
Plasma
membrane
Figure 43.9 Antigen receptors on lymphocytes
B cell
Cytoplasm of B cell
Cytoplasm of T cell
T cell
(a) B cell receptor
(b) T cell receptor

11. B Cells Antigen-specific B cell receptor
Class II MHC and processed antigen are displayed
Antigen
Antibodies
(Immunoglobins)
B cell
Cytokines (Lymphokines)
Plasma cell
B cells work chiefly by secreting soluble substances known as antibodies. They mill around a lymph node, waiting for a macrophage to bring an antigen or for an invader such as a bacteria to arrive. When an antigen-specific antibody on a B cell matches up with an antigen, a remarkable transformation occurs.
The antigen binds to the antibody receptor, the B cell engulfs it, and, after a special helper T cell joins the action, the B cell becomes a large plasma cell factory that produces identical copies of specific antibody molecules at an astonishing pace--up to 10 million copies an hour.
Antibodies belong to a family of large protein molecules known as immunoglobulins.
Scientists have identified nine chemically distinct classes of human immunoglobulins, four kinds of IgG and two kinds of IgA, plus IgM, IgE, and IgD.
Immunoglobulins G, D, and E are similar in appearance. IgG, the major immunoglobulin in the blood, is also able to enter tissue spaces; it works efficiently to coat microorganisms, speeding their destruction by other cells in the immune system. IgD is almost exclusively found inserted into the membrane of B cells, where it somehow regulates the cell’s activation. IgE is normally present in only trace amounts, but it is responsible for the symptoms of allergy.
IgA--a doublet--guards the entrance to the body. It concentrates in body fluids such as tears, saliva, and secretions of the respiratory and gastrointestinal tracts.
IgM usually combines in star-shaped clusters. It tends to remain in the bloodstream, where it is very effective in killing bacteria.
bacteria
Activated helper T cell

12. Resting cytotoxic T cell Activated helper T cell
T Cells
Resting helper T cell
Resting cytotoxic T cell
Cytokines
Released by
Helper T-Cells
Granule w/
destructive
enzymes
T cells contribute to your immune defenses in two major ways. Some help regulate the complex workings of the overall immune response, while others are cytotoxic and directly contact infected cells and destroy them.
Chief among the regulatory T cells are helper T cells. They are needed to activate many immune cells, including B cells and other T cells.
Cytotoxic T cells (sometimes called killer T cells) help rid your body of cells that have been infected by viruses as well as cells that have been transformed by cancer but have not yet adapted to evade the immune detection system. They are also responsible for the rejection of tissue and organ grafts.
Activated helper T cell
Activated killer cell
Activated when they encounter infected cells that are presenting antigens

13. Killer Cells: Cytotoxic Ts
Target cell
Target-oriented granules
Surface contact
At least two types of lymphocytes are killer cells--cytotoxic T cells and natural killer cells. Both types contain granules filled with potent chemicals. Both types kill on contact. They bind their targets, aim their weapons, and deliver bursts of lethal chemicals.
To attack, cytotoxic T cells need to recognize a specific antigen bound to self-MHC markers, whereas natural killer (NK) cells will recognize and attack cells lacking these. This gives NK cells the potential to attack many types of foreign cells.

14. Infected cell Microbe Antigen- presenting cell 1 Antigen associates
Fig
Infected cell
Microbe
Antigen-
presenting
cell 1
Antigen
associates
with MHC
molecule
Antigen
fragment
Antigen
fragment 1 1
Class I MHC
molecule
Class II MHC
molecule 2 2
T cell
receptor
T cell
receptor 2
T cell
recognizes
combination
(a)
Cytotoxic T cell
(b)
Helper T cell

15. Activation of B Cells to Make Antibody Antigen-presenting cell
Circulating antibody
Antigen
Antigen-specific B cell receptor
Class II MHC and processed antigen are displayed
Antigen-presenting cell
Antigen is processed
Antigen
Class II MHC
The B cell uses its antibody-receptor to bind a matching antigen, which it then engulfs and processes. This triggers the B cell to become a large plasma cell producing millions of copies of the same specific antibody. These antibodies then circulate in the bloodstream in search of more matching antigens. B cell antibodies cannot themselves kill an invading organism, but they can use their antibodies to mark invaders for destruction by other immune cells and by complement.
Cytokines
B cell
Antibodies
Antigen-presenting cell
Activated helper T cell
Plasma cell

16. Animation: Role of B Cells
Fig
Antigen molecules
B cells that
differ in
antigen
specificity
Antigen
receptor
Figure Clonal selection of B cells
Antibody
molecules
Clone of memory B cells
Clone of plasma cells

17. Figure 43.16 An overview of the acquired immune response
Humoral (antibody-mediated) immune response
Cell-mediated immune response
Key
Antigen (1st exposure) +
Stimulates
Gives rise to
Engulfed by
Antigen-
presenting cell + + +
B cell
Helper T cell
Cytotoxic T cell + +
Memory
Helper T cells + + +
Figure An overview of the acquired immune response
Antigen (2nd exposure) +
Memory
Cytotoxic T cells
Active
Cytotoxic T cells
Plasma cells
Memory B cells
Secreted
antibodies
Defend against extracellular pathogens by binding to antigens,
thereby neutralizing pathogens or making them better targets
for phagocytes and complement proteins.
Defend against intracellular pathogens
and cancer by binding to and lysing the
infected cells or cancer cells.

18. Helper T Cells Antigen- presenting cell Peptide antigen Bacterium
Fig
Helper T Cells
Antigen-
presenting
cell
Peptide antigen
Bacterium
Class II MHC molecule
CD4
TCR (T cell receptor)
Helper T cell
Cytokines +
Humoral
immunity
(secretion of
antibodies by
plasma cells) +
Cell-mediated
immunity
(attack on
infected cells) + +
B cell
Cytotoxic T cell

19. Released cytotoxic T cell
Fig
Released cytotoxic T cell
Cytotoxic T cell
Perforin
Granzymes
CD8
TCR
Dying target cell
Class I MHC
molecule
Pore
Figure The killing action of cytotoxic T cells
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Target
cell
Peptide
antigen

20. Antigen-presenting cell Bacterium
Fig
Antigen-presenting cell
Bacterium
Peptide
antigen
B cell
Class II MHC
molecule +
Clone of plasma cells
Secreted
antibody
molecules
Cytokines
TCR
CD4
Endoplasmic
reticulum of
plasma cell
Activated
helper T cell
Helper T cell
Clone of memory
B cells
Figure B cell activation in the humoral immune response
2 µm

21. Figure 43.21 Antibody-mediated mechanisms of antigen disposal
Viral neutralization
Opsonization
Activation of complement system and pore formation
Bacterium
Complement proteins
Virus
Formation of
membrane
attack complex
Flow of water
and ions
Macrophage
Pore
Figure Antibody-mediated mechanisms of antigen disposal
Foreign
cell